Flooded heat exchangers are known for use in heat exchange systems such as for heating water, such as in hotels or industrial environments. A flooded heat exchanger comprises a water side and a steam side that are in heat exchange communication with each other, for heating the water with the steam through heat exchange in respective, distinct fluid circuits. As the steam flows through the steam side it condensates to form condensate that flows out of the heat exchanger. The change of phase of the gaseous steam into liquid condensate is highly exothermic and allows the transfer of a significant quantity of energy from the steam to the water to be heated. A valve is installed on the steam side, at the outlet of the heat exchanger, to control the level of condensate being outputted. This allows the level of condensate to be adjusted on the steam side: if the proportion of steam on the steam side is more important, the heat transfer will be more important due to the hotter steam transferring more energy to the water. However, if the condensate is proportionately more important, then the heat transfer will be less important. The variation in the level of condensate on the steam side, is called the level of flooding of the heat exchanger. It is known to calibrate the level of flooding to adjust the heat exchange, to accommodate variations in the demand in hot water on the water side.
These flooded heat exchangers are so-called feedback heat exchangers, in that the temperature at the heated water outlet will be continuously measured to consequently control the control valve to in turn control the level of flooding according to the demand in hot water at the heated water outlet.
One problem with prior art heat exchangers is linked to energy loss related to flash steam at the condensate output line. This energy loss is typically between 3.9% for heat exchangers that operate at 15 psi; to about 6.5% for heat exchangers that operate at 30 psi. The flash steam in the condensate output line is mainly the result of the condensate exiting the heat exchanger at about the saturation temperature. For example, in a heat exchanger that operates at 15 psi, the steam and condensate temperatures are both 250° F., and the energy loss is about 3.9%; while for heat exchangers that operate at 30 psi, the steam and condensate temperatures are both 274° F., and the energy loss is about 6.5%.